Lower chamber heaters for improved etch processes

ABSTRACT

A method of improving a plasma etch chamber by installing heaters on outer surfaces. A method of improving STI etch. A method of improving STI etch in a Hitachi M700 series etcher.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under U.S.C. §119(e) ofU.S. Provisional Application 61/249,387 (Texas Instruments docket numberTI-68259, filed Oct. 7, 2009.

FIELD OF THE INVENTION

This invention relates generally to an etching process chamber and moreparticularly to a temperature control assembly for use in etchingprocesses.

BACKGROUND OF THE INVENTION

Plasma etching of semiconductor materials is typically performed in aplasma etching chamber that has gas inlet ports, gas exhaust ports, amechanism for transporting wafers into and out of the etching chamber,and a pedestal on which the wafer rests while being etched. Typically toaccelerate the etching rate, portions of the etching chamber may beheated. Gaseous reactants typically contain carbon. Products of theetching reaction that are in the plasma may further react to form apolymeric material that may deposit on the sidewalls of thesemiconductor geometries being etched and may also deposit on interiorsurfaces of the etching chamber. This polymeric deposition maybe used tocontrol the sidewall profile geometries being etched. Etch productdeposition on the walls of the chamber may build up and startdelaminating causing particulates. These particulates may deposit on thewafer during etch causing blocked etch defects and may deposit on thewafer post etch causing defects that later result in circuit failureduring electrical test. Running additional chamber cleaning cycles andopening the chamber to perform preventative maintenance (PM) to removethe deposition reduces machine availability and increases manufacturingcost. Particle defects reduce yield also increasing manufacturing cost.

Additionally, build up of deposition within the etch chamber may changethe performance of the etching as more wafers are etched resulting inmore variability in the critical dimension, CD, or sidewall profile ofthe geometry being formed.

SUMMARY OF THE INVENTION

The following presents a simplified summary in order to provide a basicunderstanding of one or more aspects of the invention. This summary isnot an extensive overview of the invention, and is neither intended toidentify key or critical elements of the invention, nor to delineate thescope thereof. Rather, the primary purpose of the summary is to presentsome concepts of the invention in a simplified form as a prelude to amore detailed description that is presented later.

Heating devices are added to the cooler portions of a Hitachi plasmaetching chamber, to the gate valve, and to the wafer transport tunnel.

DESCRIPTION OF THE VIEWS OF THE DRAWING

FIG. 1 (Prior art) is a cross-section of an example etch chamber

FIG. 2 is a cross-section of an example etch chamber according to anembodiment.

FIG. 3 is a plot of linewidth comparing the variation in a line formedwith and without an embodiment.

FIG. 4 is a plot of particles formed during etching before and afterimplementation of an embodiment.

FIG. 5 (Prior art) is a crossection of a semiconductor deviceillustrating an STI structure.

DETAILED DESCRIPTION

The present invention is described with reference to the attachedfigures, wherein like reference numerals are used throughout the figuresto designate similar or equivalent elements. The figures are not drawnto scale and they are provided merely to illustrate the invention.Several aspects of the invention are described below with reference toexample applications for illustration. It should be understood thatnumerous specific details, relationships, and methods are set forth toprovide an understanding of the invention. One skilled in the relevantart, however, will readily recognize that the invention can be practicedwithout one or more of the specific details or with other methods. Inother instances, well-known structures or operations are not shown indetail to avoid obscuring the invention. The present invention is notlimited by the illustrated ordering of acts or events, as some acts mayoccur in different orders and/or concurrently with other acts or events.Furthermore, not all illustrated acts or events are required toimplement a methodology in accordance with the present invention.

Polymer or process deposition occurs in a number of plasma etchesperformed in Hitachi etchers such as the shallow trench isolation (STI)etch and aluminum metal etch. This deposition may occur on the insidewalls of the etch chamber, especially in the cooler regions. Thisdeposition may build up and delaminate depositing particulates onto thewafer during or post etch which result in defects that may limit yield.In addition, build up of the deposition on the inside walls of thechamber may change the etch performance resulting in increasedvariability in the critical dimension, CD, of the geometry being formed.

Although STI etch in a Hitachi M-712 is used as an embodiment toillustrate the instant invention, any etch process that deposits polymeror process films on the inner walls of a Hitachi etch chamber may alsobe used.

A cross sectional diagram of a Hitachi M-712 STI etch chamber is shownin FIG. 1. The wafer being etched, 1006, sets atop the wafer pedestal,1002. Wafers are brought into and out of the chamber through wafertransport tunnel, 1008, and isolation valve, 1014. Isolation valve,1010, may be open while the wafer is being loaded and unloaded from thechamber and may be closed during etch processing. Vacuum valve, 1010,may be open during normal processing and closed when the chamber isopened for cleaning or maintenance.

As shown in FIG. 1, because the lower portion of the STI etch chamber,is cooler than the upper portion, films formed from etching products inthe plasma may deposit on the inner walls, 1012, and on valve surfaces,1014. These deposits may cause the process performance to change as thedeposition gets thicker and may also delaminate depositing particles onthe wafer resulting in defects which may reduce yield.

In FIG. 2, heaters have been added to the lower portion of the chamber,2002 and 2006, and the wafer transport tunnel 2002. These heaters, warmthe outer surface of these areas to about 35 C or more. The preferredtemperature of the outside surfaces is about 65 C. In a preferredembodiment, the heaters are heater blankets that are custom made by TGM,Inc., of Richardson, TX, to custom fit the lower chamber surfaces, 2002and 2006, and the wafer transport tunnel, 2002 of the Hitachi M-712etching chamber.

As mention before, the deposition buildup in the chamber may change theperformance of the etch over time as more and more wafers are processed.FIG. 3 is a plot of a critical dimension, CD, line width vs time for twotime periods, 3002 and 3004, prior to the heater installation and fortwo time periods, 3006 and 3008, after the heater installation. Prior toheater installation, the CD ranged from the lower specification limit,3018, to the upper specification limit, 3024. In addition, this changeof CD in the first interval, 3002, between chamber wet cleans, 3010 and3012, is 3 weeks. In the second interval, 3004, between chamber wetcleans, 3012 and 3014, the CD change occurred in just 2.5 weeks. Withthe heaters turned on, the CD during time periods, 3006 and 3008remained for the most part between the lower control limit, 3020, andthe upper control limit, 3022. The interval between wet cleans, 3014 and3016, during the first time period with the heaters installed is 4.5weeks and the interval after wet clean 3016 during the second timeperiod with the heaters installed is more than 5 weeks. With the heatersinstalled, process performance is improved and the time between chamberwet cleans in significantly improved. The improved CD control improvesyield by reducing STI voids and extends time between wet cleansimproving equipment uptime thus reducing manufacturing cost.

Particles per wafer vs time between wet cleans is shown in FIG. 4.Heaters were not installed on the Hitachi M-712 STI etch chamber duringthe first interval, 3002, between wet cleans at 0 weeks and at 4 weeksand also during the second interval, 3004, between wet cleans at 4 weeksand at 7 weeks. Particles exceeded the upper control limit, 3010, andupper specification limit, 3012, many time during these two intervals.Heaters were installed during interval, 3006, after the wet clean atweek 7 and also during interval, 3008, after wet clean at week 11.Particles with the heater installed are much reduced exceeding the uppercontrol limit only a few times and exceeding the upper specificationlimit only one time during these two intervals, 3006 and 3008. Thereduced particle count is evidence of reduced deposition within thechamber. Yield is improved by reducing particle related defects such asblocked etch and embedded particles and machine uptime is also improved.

The STI etch may consist of a series of etching steps to etch through abottom antireflective coating (BARC), 5008, a silicon nitride layer,5008, a pad oxide layer, 5004, and silicon substrate, 5002. As shown inFIG. 5, STI resist pattern, 5010, is formed on silicon substrate, 5002,and the STI etch is performed to etch STI trenches, 5012. In a preferredembodiment, heaters were installed on Hitachi M-712 etch chamber and theBARC etch endpoint time range was reduced from 2.1 to 1.1 seconds, thenitride etch endpoint time was reduced from 1.8 to 1.0 seconds, theaverage particle defectivity per wafer was reduced from 35 to 10particles per wafer, the blocked etch defects were reduced from 5.7 to0.6 per wafer, wafers scrapped due to blocked etch defects was reducedfrom 5 to 1 wafer per month, the margin for STI voids was improved by 10times, and the number of wet cleans was reduced from 42 to 28 per year.Manufacturing cost was significantly reduced with improved yield andwith improved machine uptime. In this embodiment the performance of theetching equipment and the STI etch is improved with no changes to theetch recipe. This also saved manufacturing cost by avoiding expensiveprocess and product requalification.

While the STI etch in a Hitachi M-712 is used to illustrate anembodiment of the instant invention, other etching chambers thatexperience deposition on chamber inside walls during etch such asaluminum metal etch may also benefit.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only and not limitation. Numerous changes to the disclosedembodiments can be made in accordance with the disclosure herein withoutdeparting from the spirit or scope of the invention. Thus, the breadthand scope of the present invention should not be limited by any of theabove described embodiments. Rather, the scope of the invention shouldbe defined in accordance with the following claims and theirequivalents.

1. A plasma etching chamber, comprising: heaters coupled to a lowerportion of said plasma etching chamber; and heaters coupled to a wafertunnel of said plasma etching chamber.
 2. The plasma etching chamber ofclaim 1 where said heaters are blanket resistance heaters.
 3. The plasmaetching chamber of claim 2 where said blanket resistance heaters aremanufactured by TGM company.
 4. The plasma etching chamber of claim 1where said plasma etching chamber is a Hitachi M700 series etch chamber.5. The plasma etching chamber of claim 1 where said plasma etchingchamber is a Hitachi aluminum metal etching chamber.
 6. A method forimproving the performance of a plasma etch, comprising: installingheaters on a lower outside surface of a plasma etching chamber; andheating said lower outside surface of said plasma etching chamber to atemperature of at least 35 C.
 7. The method of claim 6 where said plasmaetch is an STI etch and where said plasma etching chamber is a HitachiM700 series etch chamber.
 8. The method of claim 6 where said heatersare blanket resistance heaters.
 9. The method of claim 8 where saidblanket resistance heaters are manufactured by TGM company.
 10. Themethod of claim 6 where said temperature is about 65 C.
 11. The methodof claim 7 where said lower outside surface includes a lower outsidesurface of said etching chamber and an outside surface of a wafertunnel.
 12. The method of claim 6 where said plasma etch is an aluminumetch in a Hitachi etching chamber.
 13. A method for improving an STIetch, comprising: installing heaters on an outside surface of an STIetching chamber; and heating said outside surface of said STI etchingchamber to a temperature of at least 35 C.
 14. The method of claim 13where said STI etching chamber is a Hitachi M700 series etch chamber.15. The method of claim 13 where said heaters are blanket resistanceheaters.
 16. The method of claim 15 where said blanket resistanceheaters are manufactured by TGM company.
 17. The method of claim 13where said temperature is about 65 C.
 18. The method of claim 13 wheresaid outside surface includes an outside surface of said etching chamberand an outside surface of a wafer tunnel.
 19. The method of claim 14where said outside surface includes a lower outside surface of saidetching chamber and an outside surface of a wafer tunnel.